DOCSLIB.ORG

Emissivity and the Fate of Pluto's Atmosphere

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Emissivity and the Fate of Pluto's Atmosphere Icarus 141, 299–306 (1999) Article ID icar.1999.6169, available online at http://www.idealibrary.com on Emissivity and the Fate of Pluto’s Atmosphere J. A. Stansberry1 Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, Arizona 86001 E-mail: [email protected] and R. V. Yelle2 Center for Space Physics, Boston University, Boston, Massachusetts 02215 Received July 30, 1998; revised February 19, 1999 out that the vapor pressure of such an atmosphere would un- We present a simplified model for seasonal changes in Pluto’s dergo large pressure changes as the temperature of the ice on surface–atmosphere system. The model demonstrates the potential the surface changed in response to eccentricity-driven changes importance of the solid-state phase transition between -N2 and in insolation. The subsequent discovery that N2 ice is much -N2, and the accompanying change in emissivity, for predicting more abundant on Pluto than CH4 ice (Owen et al. 1993) means the seasonal bulk of Pluto’s (and Triton’s) atmosphere. Specifically, that Pluto’s atmosphere is dominated by N2 (its vapor pressure is the model shows that under simplified but not unreasonable as- 4 '10 times larger than that of CH4 at Pluto temperatures (Brown sumptions Pluto may have nearly the same atmospheric pressure and Ziegler 1979)), but does not change the expectation of sea- at aphelion as it does now, near perihelion. The emissivity change sonally induced pressure oscillations, because N will also form which accompanies the – phase change should be included in 2 the next generation of Pluto and Triton seasonal models for the a vapor-pressure atmosphere. purposes of understanding the evolution of their atmospheres over Observations pertaining to the pressure of Pluto’s atmosphere seasonal and climatic timescales. c 1999 Academic Press and the temperature of its N2 ice are consistent with vapor- Key Words: Pluto; Pluto, atmosphere; Pluto, surface; Triton; pressure equilibrium. A stellar occultation by Pluto in 1988 atmospheres, evolution. set a lower limit on the perihelion surface pressure of 3 bar (Elliot et al. 1989, Hubbard et al. 1989, Elliot and Young 1992, Millis et al. 1993). Stansberry et al. (1994) argued that INTRODUCTION the occultation may not have reached Pluto’s surface, and that Pluto posesses a deep (50 km) troposphere. This hypothe- Pluto’s orbital eccentricity (0.25) means that it recieves 2.8 sis, strengthened by recent results indicating that Triton’s at- times as much sunlight at perihelion (which occurred in 1989) mosphere may now posess a troposphere approximately 50 km as it does at aphelion. The idea that this extreme insolation varia- deep (Elliot et al. 1999) implies that the true surface pressure of tion might lead to extreme changes in the bulk of the atmosphere N2 on Pluto is nearer 19 bar. Tryka et al. (1993) also argued followed close on the heels of the realization that Pluto posesses for a higher surface pressure, near 60 bar, on the basis of the an atmosphere. Cruikshank et al. (1976) discovered absorption observed shape of the N2 ice absorption feature. These pressures features in Pluto’s near-IR spectrum which were eventually at- correspond to the vapor pressure of N2 over a temperature range tributed to the presence of CH4 ice (Cruikshank and Apt 1984). of 35–40 K (Brown and Ziegler 1979). This is in excellent agree- Although the observed spectrum was due solely to absorption ment with temperatures calculated on the basis of surface en- by ice, it meant that Pluto had at least a tenuous CH4 atmo- ergy balance (Stansberry et al. 1994), and is not inconsistent with sphere because CH4 has a significant (0.1–100 bar) vapor pres- temperatures derived from far-IR observations of emission from sure at temperatures then predicted for Pluto (Cruikshank and Pluto (Altenhoff et al. 1988, Jewitt 1994, Stern et al. 1993, Tryka Silvaggio 1979, Trafton 1980). Stern and Trafton (1984) pointed et al. 1994, Spencer et al. 1997). Phase equilibrium is usually encountered in systems consid- 1 erably smaller than the entire surface–atmosphere interface of Current address: Steward Observatory, University of Arizona, 933 N. a planet (although Triton is another example of such a situ- Cherry Avenue, Tucson, AZ 85721. 2 Current address: Department of Physics and Astronomy, Northern Arizona ation). Despite the large scale of this system, the conditions University, Flagstaff, AZ 86011. of vapor–solid phase equilibrium, namely a single pressure and 299 0019-1035/99 $30.00 Copyright c 1999 by Academic Press All rights of reproduction in any form reserved. 300 STANSBERRY AND YELLE temperature, have been theoretically shown to apply to the entire The term is the ratio of the total area of the N2 ice to its cross- ice–atmosphere interface (Leighton and Murray 1966, Trafton sectional area as viewed from the Sun; i.e., it is the ratio of the 1984, Yelle et al. 1995). Thus, a variety of observations and the- area over which thermal reradiation from the ice occurs to the ory are consistent with the idea that Pluto’s near-perihelion atmo- area receiving sunlight. sphere is in equilibrium with the surface N2 ice. We note that the We wish to use these relations to predict the seasonal vari- dual-volatile seasonal model of Trafton (1990) leads to atmo- ability of the temperature of Pluto’s N2 ice, and thereby the at- spheric pressures of N2 considerably lower than those derived mospheric pressure. In order to do so we must know the values from the single-volatile considerations above, and that the of the albedo, emissivity, and as a function of time. Volatile Trafton model gives results consistent with a 3-bar surface tranport models have been used to predict the distribution of pressure for Pluto (Trafton et al. 1998). That model is also of in- N2 ice, i.e., , as a function of time under the assumption of terest because, like the model we present here, it predicts that un- constant frost albedo and emissivity (Spencer 1990; Stansberry der certain conditions Pluto’s atmosphere may not freeze out at et al. 1990; Hansen and Paige 1992, 1996; Brown and Kirk aphelion. However, the other dual-volatile model for Triton and 1994). In general these models do a poor job of both explain- Pluto (Stansberry et al. 1996b, Trafton et al. 1998) comes to dif- ing the observed albedo patterns on Triton and predicting the ferent conclusions, so for current purposes we will assume that changes in atmospheric pressure which have now been detected single-phase vapor-pressure equilibrium is an adequate para- on Triton (Elliot et al. 1997, 1998). There is no reason to expect digm for exploring the seasonal evolution of Pluto’s atmospheric them to perform better on Pluto. Because our primary interest in pressure. this study is to examine the effect of emissivity on the seasonal frost temperature, and because existing volatile transport mod- THERMAL MODEL els are of limited utility in predicting the time behavior of ,we simply take = 4 in our models, equivalent to assuming that the Nitrogen ice everywhere on the surface of Pluto is at the entire planet is covered by N2 ice. Later we discuss how changes same temperature because sublimation, atmospheric transport, in due to volatile transport would influence our results. We fur- and condensation act to efficiently redistribute energy across the ther assume that N2 ice has a bolometric albedo of 0.8, based globe (e.g., Spencer et al. 1997 and references therein). The usual on Voyager imaging results from Triton (Stansberry et al. 1990) equation for the diurnally averaged equilibrium temperaure of and mutual event albedo maps of Pluto (Stansberry et al. 1994). the surface, as a function of latitude (), The detailed emissivity behavior of the N2 is discussed below. As noted above, Eqs. (1)–(3) are only applicable if the condi- Z 1 T 4 = , tion of frost isothermality is satisfied. The amount of latent heat Teq( ) S0(1 A) d cos (1) T that can be transported around the globe by winds of a given velocity dependens upon the atmospheric density: as the atmo- where is the emissivity of the ice, is the Stefan–Boltzmann spheric pressure falls, winds will grow stronger. When the wind constant, Teq is the radiative equilibrium temperature of the sur- speed begins to approach the sound speed, significant pressure face, S0 is the solar flux at Pluto, A is the bolometric albedo of gradients will be required to drive the flow (Trafton and Stern the ice (which we set to 0.8), is longitude, T is the longi- 1983, Yelle et al. 1995). The presence of significant pressure tude of the terminator at a given latitude, and is the local solar differences in the atmosphere implies temperature differences zenith angle, must be modified to account for the latent heat flux between different regions of N2 ice on the surface with which in the equation of local energy balance. Writing the cossine of the atmosphere is in contact; i.e., the condition of isothermal- the diurnally averaged solar zenith angle (the integral in Eq. (1)) ity is violated. Spencer et al. (1997) show that the condition of as ¯ gives isothermality breaks down when the N2 ice temperature falls below about 31 K, with a corresponding atmospheric pressure S ¯ (1 A) = T 4 + Lm˙ , (2) 0 of 0.1 bar. where L is the latent heat of sublimation per unit mass of N2 9 1 (2.6 10 erg/g ) (Brown and Ziegler 1979), and m˙ is the sub- EMISSIVITY AND THE – PHASE TRANSITION limation mass flux. For current conditions on Pluto the temper- ature of the N2 is the same everywhere to within a small fraction The N2 – solid phase transition occurs at T = 35.6 K, of a Kelvin (Yelle et al.
Load more

Recommended publications
  • Earth-Sun Relationships
    EARTH-SUN RELATIONSHIPS UNIT OBJECTIVES • EXPLAIN THE EFFECTS OF THE EARTH-SUN RELATIONSHIP ON LIFE ON EARTH. • IDENTIFY THE FACTORS THAT CONTRIBUTE TO EARTH’S CLIMATES. • DESCRIBE THE MAJOR CLIMATE PATTERNS FOUND ON EARTH. EARTH-SUN RELATIONSHIPS OBJECTIVES • DESCRIBE HOW EARTH’S POSITION IN RELATION TO THE SUN AFFECTS TEMPERATURES ON EARTH. • EXPLAIN HOW EARTH’S ROTATION CAUSES DAY AND NIGHT. • DISCUSS THE RELATIONSHIP OF THE EARTH TO THE SUN DURING EACH SEASON. • IDENTIFY HOW GLOBAL WARMING MIGHT AFFECT EARTH’S AIR, LAND, AND WATER. EARTH-SUN RELATIONSHIPS TERMS TO KNOW PLACES TO LOCATE CLIMATE SEASONS TROPIC OF CANCER AXIS ECLIPTIC TROPIC OF CAPRICORN TEMPERATURE ENERGY EQUATOR REVOLUTION ROTATION POLES EQUINOX CONDUCTOR SOLSTICE CONVECTION GREENHOUSE EFFECT ADVECTION GLOBAL WARMING RADIATION WEATHER PERIHELION APHELION EARTH-SUN RELATIONSHIPS THE SUN, THE BRIGHTEST STAR IN OUR SKY, IS A MAJOR FACTOR IN CREATING EARTH’S CLIMATES. THE SUN, COMPOSED OF HYDROGEN, HELIUM, AND OTHER GASES, ROTATES ON AN AXIS AT ABOUT THE SAME ANGLE AS THE EARTH’S AXIS. ONLY A TINY FRACTION OF THE POWER GENERATED BY THE SUN REACHES THE EARTH. OUR SOLAR SYSTEM DIMENSIONS AND DISTANCES • EARTH’S ORBIT • AVERAGE DISTANCE FROM EARTH TO THE SUN IS 150,000,000 KM (93,000,000 MI). • PERIHELION • CLOSEST AT JANUARY 3. • 147,255,000 KM (91,500,000 MI). • APHELION • FARTHEST AT JULY 4. • 152,083,000 KM (94,500,000 MI). • EARTH IS 8 MINUTES 20 SECONDS FROM THE SUN. • PLANE OF EARTH’S ORBIT IS THE PLANE OF THE ECLIPTIC. EARTH’S TILT AND ROTATION • EARTH IS CURRENTLY TILTED AT AN ANGLE OF ABOUT 23½°.
    [Show full text]
  • Name Period the Seasons on Earth
    Name Period The Seasons on Earth – Note Taking Guide DIRECTIONS: Fill in the blanks below, using the word bank provided. Label all latitudes shown in the diagram. Axis 0o Arctic Circle Changes 23.5o N Antarctic Circle Daylight 23.5o S North Pole Length 66.5o N South Pole Seasons 66.5o S Equator Tilted 90o N Tropic of Cancer 23.5o 90o S Tropic of Capricorn 1. The earth is on its axis . 2. The tilt effects the of our days and causes the of our . 3. 4. Solar flux describes . 5. When only a small amount of light hits a surface there is . 6. Solar flux effects the of a surface. 7. Low flux will make a surface and high flux will make a surface . 8. What two factors cause solar flux to be lower at higher latitudes? DIRECTION: Fill in as much information as you can about the movement of our planet around the Sun. The word bank below will help you get started. You should be able to fill in every blank line provided. 1. Earth’s orbit around the sun is nearly . 2. Earth is closest to the sun during N. Hemisphere . This is . 3. Earth is farthest away from the sun during N. Hemisphere . This is . Circular Aphelion March 22nd Elliptical Summer Solstice September 22nd Orbit Winter Solstice June 22nd Tilted Vernal Equinox December 22nd Perihelion Autumnal Equinox Sun Name KEY Period The Seasons on Earth – Note Taking Guide DIRECTIONS: Fill in the blanks below, using the word bank provided. Label all latitudes shown in the diagram.
    [Show full text]
  • On the Choice of Average Solar Zenith Angle
    2994 JOURNAL OF THE ATMOSPHERIC SCIENCES VOLUME 71 On the Choice of Average Solar Zenith Angle TIMOTHY W. CRONIN Program in Atmospheres, Oceans, and Climate, Massachusetts Institute of Technology, Cambridge, Massachusetts (Manuscript received 6 December 2013, in final form 19 March 2014) ABSTRACT Idealized climate modeling studies often choose to neglect spatiotemporal variations in solar radiation, but doing so comes with an important decision about how to average solar radiation in space and time. Since both clear-sky and cloud albedo are increasing functions of the solar zenith angle, one can choose an absorption- weighted zenith angle that reproduces the spatial- or time-mean absorbed solar radiation. Calculations are performed for a pure scattering atmosphere and with a more detailed radiative transfer model and show that the absorption-weighted zenith angle is usually between the daytime-weighted and insolation-weighted zenith angles but much closer to the insolation-weighted zenith angle in most cases, especially if clouds are re- sponsible for much of the shortwave reflection. Use of daytime-average zenith angle may lead to a high bias in planetary albedo of approximately 3%, equivalent to a deficit in shortwave absorption of approximately 22 10 W m in the global energy budget (comparable to the radiative forcing of a roughly sixfold change in CO2 concentration). Other studies that have used general circulation models with spatially constant insolation have underestimated the global-mean zenith angle, with a consequent low bias in planetary albedo of ap- 2 proximately 2%–6% or a surplus in shortwave absorption of approximately 7–20 W m 2 in the global energy budget.
    [Show full text]
  • Elemental Geosystems, 5E (Christopherson) Chapter 2 Solar Energy, Seasons, and the Atmosphere
    Elemental Geosystems, 5e (Christopherson) Chapter 2 Solar Energy, Seasons, and the Atmosphere 1) Our planet and our lives are powered by A) energy derived from inside Earth. B) radiant energy from the Sun. C) utilities and oil companies. D) shorter wavelengths of gamma rays, X-rays, and ultraviolet. Answer: B 2) Which of the following is true? A) The Sun is the largest star in the Milky Way Galaxy. B) The Milky Way is part of our Solar System. C) The Sun produces energy through fusion processes. D) The Sun is also a planet. Answer: C 3) Which of the following is true about the Milky Way galaxy in which we live? A) It is a spiral-shaped galaxy. B) It is one of millions of galaxies in the universe. C) It contains approximately 400 billion stars. D) All of the above are true. E) Only A and B are true. Answer: D 4) The planetesimal hypothesis pertains to the formation of the A) universe. B) galaxy. C) planets. D) ocean basins. Answer: C 5) The flattened structure of the Milky Way is revealed by A) the constellations of the Zodiac. B) a narrow band of hazy light that stretches across the night sky. C) the alignment of the planets in the solar system. D) the plane of the ecliptic. Answer: B 6) Earth and the Sun formed specifically from A) the galaxy. B) unknown origins. C) a nebula of dust and gases. D) other planets. Answer: C 7) Which of the following is not true of stars? A) They form in great clouds of gas and dust known as nebula.
    [Show full text]
  • Earth-Sun Relationship
    Geog 210 Assignment 1 Summer 2004 Earth-Sun Relationship Due Date: Thursday June 24, 2004 *** Angles should NOT exceed 90º nor negative!!!. NAME ___________________ EQUINOXES – March 21 or September 23 At what latitude is the noon sun directly 1. Introduction overhead on this date? ___________ The purpose of this assignment is to introduce What is the noon sun angle (altitude) for you to some of the important aspects of earth- sun relationship. In class I showed the 90 ºN ________ 23.5 ºS ________ seasonal path of the earth using the globe and 66.5 ºN ________ 40 ºS ________ slide projector (sun). Make sure that you need 40 ºN ________ 66.5 ºS ________ to understand these fundamental relationships 23.5 ºN ________ 90 ºS ________ by drawing and labeling the relative 0 ºN ________ positions of the following features: Earth’s axis, North and South Poles, Equator, circle of illumination, subsolar point, Tropic of Cancer and Capricorn, Arctic and Antarctic Sun’s Rays Circles. Use the circles provided in the next section to draw these for all three cases. (each 1 point, 10 points total for each diagram) 2. Sun angle As you recall, the earth’s axis remains a constant tilt with respect to the solar system as OUR SUMMER SOLSTICE – June 21 the Earth revolves (axial parallelism). Thus, the latitude of the subsolar point, known as the At what latitude is the noon sun directly Sun’s declination, changes with seasons, and overhead on this date? ___________ the angle of the sun’s rays striking any given place on Earth changes throughout the year.
    [Show full text]
  • A Theoretical Study of the Global F Region for June Solstice, Solar Maximum, and Low Magnetic Activity
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 90, NO. A6, PAGES 5285-5298, JUNE 1, 1985 A Theoretical Study of the Global F Region for June Solstice, Solar Maximum, and Low Magnetic Activity J. J. SOJKA AND R. W. SCHUNK Center for Atmospheric and Space Sciences, Utah State University. Logan We constructed a time-dependent, three-dimensional, multi-ion numerical model of the global ionosphere at F region altitudes. The model takes account of all the processes included in the existing regional models of the ionosphere. The inputs needed for our global model are the neutral temperature, composition, and wind; the magnetospheric and equato ~ ial . electric field distributions; th.e auror!l precipitation pattern; the solar EUV spectrum; and a magnetic field model. The model produces IOn (NO , O ~ , N ~, N+, 0+, He +) density distributions as a function of time. For our first global study, we selected solar maximum. low geomagnetic activity, and June solstice conditions. From this study we found the following: (I) The global ionosphere exhibits an appreciable UT variation, with the largest variation occurring in the southern winter hemisphere; (2) At a given time, Nm F2 varies by almost three orders of magnitude over the globe, with the largest densities (5 x 106 cm-J) occurring in the equatorial region and. t~e lo~est (7. x 10J cm-J) in the southern hemisphere mid-latitude trough; (3) Our Appleton peak charactenstlcs differ shghtly from those obtained in previous model studies owing to our adopted equatorial electric field distribution, but the existing data are not sufficient to resolve the differences between the models; (4) Interhemispheric flow has an appreciable effect on the F region below about 25 0 magnetic la.titude; (5) In the southern wi~ter hemisphere, the mid-latitude trough nearly circles the globe.
    [Show full text]
  • 0 the Shape and Logatxon of the Diurnal
    tft LLI -0 a n 0 0. (3 THE SHAPE AND LOGATXON OF THE DIURNAL ITHRUl IICODE) (CATEGORY) . .. .. - .. SA0 Special Report No. 207 THE SHAPE AND LOCATION OF THE DIURNAL BULGE IN THE UPPER ATMOSPHERE L. G. Jacchia and J. Slowey Smithsonian Institution Astrophysical Observatory Cambridge, Massachusetts 02 138 3-66-29 TABLE OF CONTENTS Section Page ABSTRACT ix 1 THE DIURNALBULGE.,..................,. 1 2 THE MODEL OF GLOBAL TEMPERATURE VARIATIONS ............................. 3 3 NUMERICAL PARAMETERS FOR THE MODEL. ..... 5 I. 4 RESULTS FROM HIGH-INCLINATION SATELLITES. .. 9 5 POSSIBLE IMPLICATIONS. ................... 17 6 REFERENCES............................ 21 V PRECEDlNGsPAGE BLANK NOT FILMED. (0- 4 LIST OF ILLUSTRATIONS Figure Page 1 Upper-air temperature distribution according to equation (2), using three different values of m. ....... 8 2 Exospheric temperatures from the drag of the Explorer 19 satellite (1963-53A). ................ 11 3 Exospheric temperatures from the drag of the Explorer 24 satellite (1964-76A). ................ 12 4 Exospheric temperatures from the drag of the Explorer 1 satellite (1958 Alpha). ................ 14 LIST OF TABLES Page II Table 1 Average departure of temperature residuals from I their mean ............................... 16 vii I- THE SHAPE AND LOCATION OF THE DIURNAL BULGE IN THE UPPER ATMOSPHERE' 3 L. G. Jacchia2 and J. Slowey ABSTRACT A= ~ndxrc;cJ "-Id the drag of thz two ballocj~isaieiiiies in near-polar orbits launched in the course of the last 2 years (Explorers 19 and 24) has afforded the opportunity of our studying the distribution of density and tempera- ture at high latitudes, and has led to strange results con- cerning the shape and behavior of the diurnal atmospheric bulge.
    [Show full text]
  • Examples in Climate Change
    CHAPTER 3 Examples in Climate Change. This Chapter includes a series of self-contained examples of the use of time series tools in the context of climate problems. Most of the material consists of published papers; the remainder discusses aspects of the study of climate with strong connection to understanding of time series. The published or submitted papers are available on line at http://puddle.mit.edu/~cwunsch. The attached papers, also available online, are Wunsch, C., On sharp spectral lines in the climate record and the millennial peak. Paleoceano., 15, 417-424, 2000. Wunsch, C., The spectral description of climate change including the 100KY energy, Clim. Dyn., DOI 10.1007/s00382-002-0279-z, 2002. Wunsch, C. and D. E. Gunn, A densely sampled core and climate variable aliasing, submitted for publication, 2002. Huybers, P. and C. Wunsch, Depth and orbital-tuning: a new chronology of glaciation and nonlinear climate change, submitted for publication, 2002. Wunsch, C., Greenland–Antarctic phase relations and millennial time-scale climate fluctuations in the Greenland cores, to be published, 2003. 99 100 3. EXAMPLES IN CLIMATE CHANGE. Notes on Combined Milankovitch and Tidal Theory 1 Carl Wunsch 1. Gravitational Tides One of the central elements of all discussions of low frequency climate change is the hypothesis that changes in the earth-sun orbital configuration influencing the solar radiation incident on the earth, has important consequences. This hypothesis has become known as the Milankovitch theory; its history is well-described by Imbrie and Imbrie (1986). A better known physical system dependent upon orbital configurations is the ordinary gravitational tides.
    [Show full text]
  • Analysis of the Changing Solar Radiation Angle on Hainan Island
    MATEC Web of Conferences 95, 18005 (2017) DOI: 10.1051/ matecconf/20179518005 ICMME 2016 Analysis of the changing Solar Radiation Angle on Hainan Island Zhiwu Ge1 , JingJingHuang2,HongxiaLi 2 and HuizhenWang2 1Hainan normal University, Physics Department, No. 99, Long Kun south road, Haikou, China 2Hainan normal University, Electronic Information and Technology Department, No. 99, Long Kun south road, Haikou, China Abstract. As the only tropical provinces in China, Hainan province has advantageous geographical location, and abundant solar energy resources. But because of Local ideas and habits, especially the lack of theoretical research on local solar resources, development and application of solar energy in Hainan is almost blank. In this paper, we studied the variation regularity of sunlight angle on Hainan tropical island, analyzed the revolution and rotation of the earth, and the change rule of sunlight angle caused by the sun's movement between the tropic of cancer and the tropic of capricorn, deduced the change rule of sunlight angle in the spring equinox, the autumnal equinox, summer solstice and winter solstice day, and got the movement rules of solar elevation angle throughout the year. Theoretic analysis is consistent with field measurement results. These rules are of importance and can effectively guide the local People's daily life and production, such as the reasonable layout of the buildings, floor distance between different heights of buildings, the direction of the lighting windows of tall buildings, installation angle of photovoltaic panels, and other similar solar energy absorbing and conversion equipment. 1 Preface angle changes from the original small to large, At noon to reach the maximum, which is the maximum altitude With the growing development of science and technology, angle of the Sun.
    [Show full text]
  • Earth-Sun Relations Homework Solar Angle
    Physical Elements (Geography 1) Name: ____________________________________ Homework #1: Earth­Sun Relations DUE: __________________ Circle Class period: 7:45 am 9:30 am 11:15 am Earth-Sun Relations Homework (Refer to the diagram below and Figures 1‐25, 1‐26, and 1‐27 on pages 20‐21 of the text.) 1. What is the latitude of the most direct rays of the Sun on June 21? Text p. 20‐21 _____________________ 2. What is the latitude of the tangent rays of the Sun in the Northern Hemisphere on June 21st? (These are the northernmost rays that just barely touch the Earth – the dashed lines in the sketch to the right.) _____________________ 3. What is the latitude of the tangent rays in the Southern Hemisphere on June 21st? _____________________ 4. Why is the June solstice associated with Northern Hemisphere summer? _____________________________________________________________________________ _____________________________________________________________________________ Notice the orientation of the Circle of Illumination on June 21st. 5. Does the equator receive more day or night on this day? _____________________ 6. Does day become longer or shorter as you move southward from the equator? _____________________ 7. a) How many hours of daylight are experienced between 66.5ºN – 90º N on June 21? _____________________ b) Why? _____________________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ Solar Angle The direct (or overhead) rays of the Sun will strike the Earth’s surface at the Tropic of Cancer (23.5ºN) on June 21, at the equator on the equinoxes, and at the Tropic of Capricorn (23.5ºS) on December 21. The latitude of these direct rays is called the declination of the Sun or the subsolar point.
    [Show full text]
  • Equinox|Solstice
    EQUINOX|SOLSTICE Since prehistory, the Summer Solstice has been seen as a significant time of year in many cultures, and has Vernal Equinox been marked by festivals and rituals. Traditionally, in many temperate regions (especially Europe), the The March or Northward Equinox is the Equinox on summer solstice is seen as the middle of summer and the Earth when the subsolar point appears to leave referred to as "midsummer". Today, however, in some the Southern Hemisphere and cross the celestial countries and calendars it is seen as the beginning of equator, heading northward as seen from Earth. The summer. March Equinox is known as the Vernal Equinox in the Northern Hemisphere and as the Autumnal Equinox in the Southern Hemisphere. The March Equinox may be taken to mark the beginning of spring and the end of winter in the Northern Hemisphere but marks the beginning of autumn and the end of summer in the Southern Hemisphere. The March Equinox can occur at any time from March 21 to March 24. In astronomy, the March Equinox is the zero point of sidereal time and, consequently, right ascension. It also serves as a reference for calendars and celebrations in many human cultures and religions. Summer Solstice Autumnal Equinox The Summer Solstice (or Estival Solstice), also known as Midsummer, occurs when one of the Earth's poles The September or Southward Equinox is the moment has its maximum tilt toward the Sun. It is described when the Sun appears to cross the celestial equator, as the longest day of the year. It happens twice yearly, heading southward.
    [Show full text]
  • Physical Geography Lab Activity #03 Due Date______
    Name______________________ Physical Geography Lab Activity #03 Due date___________ Navigation COR Objective 2, SLO 2 3.1. Introduction In the previous lab you learned how to use latitude and longitude to find a location on a map or globe, but what if you didn’t have those coordinates to begin with? Imagine being on a ship out in the middle of the Atlantic Ocean with no idea as to where you were exactly. Are you close to land? Are you dangerously close to jagged coastal rocks? Ptolemy developed our system of the graticule back in the year A.D. 2. The ability to actually measure the graticule out in the real world didn’t come for another 1,700 years. This lab will introduce you the basic theories behind locating your latitude and longitude using the shape of the Earth and our place in the solar system. Yes, GPS can tell us where we are, but electronics aren’t always reliable. Plus it’s way cooler to navigate using the stars… 3.2. Latitude The ability to find one’s latitude came before longitude. We can use the angle of the stars in the sky to calculate our angle of latitude. For this lab we will use the sun, but both Polaris (the North Star) and the Southern Cross constellation can be used depending on your hemisphere. 3.3. The Analemma The one trick with using the sun to measure your latitude is that you need to take into account the changing declination of the sun throughout the year. Fortunately, we have the Analemma, a lopsided figure 8 the charts the subsolar point for every day of the year (see figure 3.1).
    [Show full text]